Solar photovoltaic cells convert light energy from photons into electrical energy through the photovoltaic effect. When photons hit the solar cell, they excite electrons which are then pulled away before they can relax, generating a current. The efficiency and performance of solar cells depends on factors like material bandgap, cell temperature, and resistance. Different cell types like single crystal, polycrystalline, and amorphous thin films are fabricated through various processes to optimize these factors and harness solar energy on a large scale.

3. ABSTRACT
 Solar photovoltaic energy conversion is a one-step conversion process which
generates electrical energy from light energy.
 Light is made up of packets of energy called Photons. When they hit a solid
surface they excite the electrons, bound into solid, up to a higher energy level in
which
they are more free to move. But these electrons relax and come back to the
ground
state within no time.
 In a photovoltaic device, however, there is some built-in asymmetry which
pulls the
excited electrons away before they can relax, and feeds them to an external
circuit.

4. BACKGROUND
 most commonly manufactured PV cells are made of crystalline silicon and
have energy conversion efficiency of 12%.
 The cost of these cells is $3 per Watt of power generated under solar AM
1.5G conditions
 these costs need to be reduced by an order of magnitude to around $0.3 per
Watt for PV cells to be competitive with other energy generation system
 reducing the costs of PV cells may be achieved if the semiconductor
were deposited from solution onto large flexible substrates in reel-to-reel
coating
 reducing the costs of PV cells may be achieved if the semiconductor
were deposited from solution onto large flexible substrates in reel-to-reel coating

5. WORKING PRINCIPLE
 PHOTOCURRENT
The photo current generated by a solar cell under illumination at short circuit
is dependent on the incident light.
The photocurrent density Jsc is
QE(E) is the probability that an incident photon of energy ‘E’ will deliver one
electron
to the external circuit.
bs(E) is the incident spectral photon flux density, the number of photons of
energy in
the range E.
QE and spectrum can be given as functions of either photon energy or
wavelength, λ

6.  DARK CURRENT AND OPEN CIRCUIT VOLTAGE
When a load is present, a potential difference develops between the terminals of
the
cell. This potential difference generates a current which acts in the opposite
direction
to the photocurrent, and the net current is reduced from its short circuit value.
This
reverse current is usually called the dark current.
Where Jo is a constant, kB is Boltzmann's constant and T is temperature in
degrees
Kelvin.
When the contacts are isolated, the potential difference has its maximum
value, the open circuit voltage Voc. This is equivalent to the condition when
the dark current and short circuit photocurrent exactly cancel out. For the
ideal diode, from ideal diode equation

7.  EFFICIENCY
The cell power density is given by P=JV
P reaches a maximum at the cell's operating point or maximum power point. This
occurs at some voltage Vm with a corresponding current density Jm.
The fill factor is defined as the ratio FF = (JmVm) / (JscVoc)
The efficiency of the cell is the power density delivered at operating point as a
fraction of the incident light power density, Ps
Efficiency is related to Jsc and Voc using FF.
These four quantities: Jsc, Voc, FF and η are the key performance characteristics
of a solar cell.

8. PERFORMANCE OF SOME TYPES OF PV CELL

9.  Non-ideal diode behaviour
The ideal diode behaviour is seldom seen. It is common for the dark current to
depend more weakly on bias. The actual dependence on V is quantified by an
ideality
factor, m and the current-voltage characteristic given by the non-ideal diode
equation,
m typically lies between 1 and 2.

11. Due to doped element gradient electron and
hole get drifted to other side that cause built in
potential at junction

12. For positive voltage current will exponential and for negative voltage it will constant negative
exponential

13. When circuit is working in 4’th quadrant power driven to circuit will be positive and in
there two case it will be negative so photovoltaic cell do work in fourth quadrant

14. DESIGN PARAMETER OF PHOTO VOLTAIC CELL

15.  To increase efficiency we use material which has proper band
gap
 To ensure full absorption of photo we use anti reflective
material on cell
 large mirrors or lenses to concentrate and focus the sunlight onto a
string of cell can be used to improve efficiency by reduction in no. of
cell
 Efficiency is inversely proportional to temperature so hight efficiency
can be achieved by keep cooling the panel
 To get maximum photon flux panel should facing to sun
 Efficiency can be maximize by multiple carrier generation by single
photon

16. Series resistance of only few ohm can seriously
cause In reduction in power loss
Resistance could be minimize by increasing cell
aria
Resistance can be further minimize by distributing
the contact over n region so current would
distributed over the surface

17. Dimension of cell should be such that generated
electron-hole pair could reach the surface before
recombination take place
So there should be proper match between diffusion
length and thickness of p region and penetration
depth 1/diff. coff.
life time of carrier is inversely proportional to
concentration of doping
Contact potential is directly propositional to doping
So there is trade-off between lifetime of Carrier and
contact potential

18.  Solar cell is simple diode with special desgin
 Enough energetic photon cause generation of electron-hole pair
 Excited electron and hole get drifted by built-in potential in depletion region
 The drift current cause current in circuit.
 Voltage across individual cell is equal to built in potential

19. TYPE OF SOLAR CELL
Single Crystal solar cells in panel
• Silicon solar cells are made using either single crystal
wafers, polycrystalline wafers or thin films
• approx. 1/3 to 1/2 of a millimeter thick
• The silicon must be of a very high purity and have a near perfect
crystal structure
Polycrystalline solar panel
• Polycrystalline wafers are made by a casting process
Amorphous-Si solar panel
• Amorphous silicon, one of the thin film technologies

20. FABRICATION
 Single Crystal solar cells
 Single crystal wafers are sliced from a large single crystal ingot
 It is a very expensive process
 The silicon must be of a very high purity and have a near perfect crystal
structure
 Polycrystalline solar
 Polycrystalline wafers are made by a casting process
 molten silicon is poured into a mould and allowed to set
 Then it is sliced into wafers
 it is not as efficient as monocrystalline cells
 The lower efficiency is due to imperfections in the crystal structure resulting
from the casting process
 Amorphous-Si solar
 Amorphous silicon is one of the thin film technologies
 It is made by depositing silicon onto a glass substrate from a reactive gas
such as silane (SiH4)

21. PN JUNCTION FORMATION
 dopant atoms introduced to create a p-type
and an n-type region
 doping can be done by high temperature
diffusion
 where the wafers are placed in a furnace
with the dopant introduced as a vapour
 Once a p-n junction is created, electrical
contacts are made to the front and the back
of the cell
 evaporating or screen printing metal on to
the wafer to form contact

22.  PV cells have a working voltage of about 0.5
 they are usually connected together in series (positive to
negative) to provide larger voltages
 low power panels are made by connecting between 3 and 12
small segments of amorphous silicon PV
 larger systems can be made by linking a number of panels
together
 PV panel array, ranging from two to many hundreds of panels
 the output voltage is limited to between 12 and 50 volts, but
with higher amperage
 This is both for safety and to minimize power losses
 Arrays of panels are being increasingly used in building
construction

24. POTENTIAL
 The photovoltaic industry is growing rapidly as concern increases about
global warming
 For most of the eighties and early nineties the major markets for solar panels
were remote area power supplies and consumer products
 However in the mid nineties a major effort was launched to develop building
integrated solar panels for grid connected applications
 energy output from PV panels will vary depending on the
orientation, location, daily weather and season
 On a clear sunny day, the power density of is approximately 1kW/m2
 The solar energy received by Earth is more than 10,000 times the current use
of fossil fuels and nuclear energy combined
 harnessing such a large potential energy source has the potential to replace a
significant amount of carbon based fuels